1. Field of the Invention
The present invention relates to head rests of vehicle seats. More particularly, the present invention relates to head rests of vehicle seats that can increase restraint performance for the heads of passengers when a vehicle collision is sensed or predicted.
2. Description of the Related Art
A head rest of a vehicle seat that can be appropriately positioned relative to a head of a passenger is already known. Such a head rest (an active head rest) can increase restraint performance for the passenger head when a vehicle collision is sensed or predicted. The head rest is taught, for example, by U.S. Pat. No. 6,402,195.
In the known head rest, the head rest includes capacitance type sensors that are embedded in a main body of the head rest. The sensors are arranged and constructed to detect the position of the passenger head. Also, the head rest main body is constructed to move vertically (up and down) toward the passenger head based on a signal from the sensor. That is, the head rest main body can move. closer to the passenger head so as to be appropriately positioned relative to the passenger head. Thus, the passenger head can be suitably held by the head rest main body when a vehicle actually collides. As a result, the passenger can be prevented from suffering a whiplash injury during a vehicle collision.
Typically, the capacitance type sensors used in the known head rest are non-contacting sensors that can detect the position of the passenger head without contacting the passenger head. However, such sensors cannot accurately detect the passenger head position if the sensors are positioned away from the passenger head over a desired distance. Therefore, if the head rest main body is positioned excessively away from the passenger head when the passenger is sitting on a vehicle seat, the head rest main body cannot be moved or actuated. Consequently, in such a case, the head rest main body cannot be appropriately positioned relative to the passenger head.